// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "cc/tiles/eviction_tile_priority_queue.h"

#include "base/memory/ptr_util.h"

namespace cc {

namespace {

    class EvictionOrderComparator {
    public:
        explicit EvictionOrderComparator(TreePriority tree_priority)
            : tree_priority_(tree_priority)
        {
        }

        bool operator()(
            const std::unique_ptr<TilingSetEvictionQueue>& a_queue,
            const std::unique_ptr<TilingSetEvictionQueue>& b_queue) const
        {
            // Note that in this function, we have to return true if and only if
            // b is strictly lower priority than a.
            const PrioritizedTile& a_tile = a_queue->Top();
            const PrioritizedTile& b_tile = b_queue->Top();

            const TilePriority& a_priority = a_tile.priority();
            const TilePriority& b_priority = b_tile.priority();
            bool prioritize_low_res = tree_priority_ == SMOOTHNESS_TAKES_PRIORITY;

            // If the priority bin differs, b is lower priority if it has the higher
            // priority bin.
            if (a_priority.priority_bin != b_priority.priority_bin)
                return b_priority.priority_bin > a_priority.priority_bin;

            // Otherwise if the resolution differs, then the order will be determined by
            // whether we prioritize low res or not.
            // TODO(vmpstr): Remove this when TilePriority is no longer a member of Tile
            // class but instead produced by the iterators.
            if (b_priority.resolution != a_priority.resolution) {
                // Non ideal resolution should be sorted higher than other resolutions.
                if (a_priority.resolution == NON_IDEAL_RESOLUTION)
                    return false;

                if (b_priority.resolution == NON_IDEAL_RESOLUTION)
                    return true;

                if (prioritize_low_res)
                    return a_priority.resolution == LOW_RESOLUTION;
                return a_priority.resolution == HIGH_RESOLUTION;
            }

            // Otherwise if the occlusion differs, b is lower priority if it is
            // occluded.
            bool a_is_occluded = a_tile.is_occluded();
            bool b_is_occluded = b_tile.is_occluded();
            if (a_is_occluded != b_is_occluded)
                return b_is_occluded;

            // b is lower priorty if it is farther from visible.
            return b_priority.distance_to_visible > a_priority.distance_to_visible;
        }

    private:
        TreePriority tree_priority_;
    };

    void CreateTilingSetEvictionQueues(
        const std::vector<PictureLayerImpl*>& layers,
        TreePriority tree_priority,
        std::vector<std::unique_ptr<TilingSetEvictionQueue>>* queues)
    {
        DCHECK(queues->empty());

        for (auto* layer : layers) {
            std::unique_ptr<TilingSetEvictionQueue> tiling_set_queue = base::MakeUnique<TilingSetEvictionQueue>(
                layer->picture_layer_tiling_set());
            // Queues will only contain non empty tiling sets.
            if (!tiling_set_queue->IsEmpty())
                queues->push_back(std::move(tiling_set_queue));
        }
        std::make_heap(queues->begin(), queues->end(),
            EvictionOrderComparator(tree_priority));
    }

} // namespace

EvictionTilePriorityQueue::EvictionTilePriorityQueue()
{
}

EvictionTilePriorityQueue::~EvictionTilePriorityQueue()
{
}

void EvictionTilePriorityQueue::Build(
    const std::vector<PictureLayerImpl*>& active_layers,
    const std::vector<PictureLayerImpl*>& pending_layers,
    TreePriority tree_priority)
{
    tree_priority_ = tree_priority;

    CreateTilingSetEvictionQueues(active_layers, tree_priority, &active_queues_);
    CreateTilingSetEvictionQueues(pending_layers, tree_priority,
        &pending_queues_);
}

bool EvictionTilePriorityQueue::IsEmpty() const
{
    return active_queues_.empty() && pending_queues_.empty();
}

const PrioritizedTile& EvictionTilePriorityQueue::Top() const
{
    DCHECK(!IsEmpty());
    const auto& next_queues = GetNextQueues();
    return next_queues.front()->Top();
}

void EvictionTilePriorityQueue::Pop()
{
    DCHECK(!IsEmpty());

    auto& next_queues = GetNextQueues();
    std::pop_heap(next_queues.begin(), next_queues.end(),
        EvictionOrderComparator(tree_priority_));
    TilingSetEvictionQueue* queue = next_queues.back().get();
    queue->Pop();

    // Remove empty queues.
    if (queue->IsEmpty()) {
        next_queues.pop_back();
    } else {
        std::push_heap(next_queues.begin(), next_queues.end(),
            EvictionOrderComparator(tree_priority_));
    }
}

std::vector<std::unique_ptr<TilingSetEvictionQueue>>&
EvictionTilePriorityQueue::GetNextQueues()
{
    const EvictionTilePriorityQueue* const_this = static_cast<const EvictionTilePriorityQueue*>(this);
    const auto& const_queues = const_this->GetNextQueues();
    return const_cast<std::vector<std::unique_ptr<TilingSetEvictionQueue>>&>(
        const_queues);
}

const std::vector<std::unique_ptr<TilingSetEvictionQueue>>&
EvictionTilePriorityQueue::GetNextQueues() const
{
    DCHECK(!IsEmpty());

    // If we only have one queue with tiles, return it.
    if (active_queues_.empty())
        return pending_queues_;
    if (pending_queues_.empty())
        return active_queues_;

    const PrioritizedTile& active_tile = active_queues_.front()->Top();
    const PrioritizedTile& pending_tile = pending_queues_.front()->Top();

    const TilePriority& active_priority = active_tile.priority();
    const TilePriority& pending_priority = pending_tile.priority();

    // If the bins are the same and activation differs, then return the tree of
    // the tile not required for activation.
    if (active_priority.priority_bin == pending_priority.priority_bin && active_tile.tile()->required_for_activation() != pending_tile.tile()->required_for_activation()) {
        return active_tile.tile()->required_for_activation() ? pending_queues_
                                                             : active_queues_;
    }

    // Return tile with a lower priority.
    if (pending_priority.IsHigherPriorityThan(active_priority))
        return active_queues_;
    return pending_queues_;
}

} // namespace cc
